ACOUSTIC WAVE DEVICES WITH RESONANCE-TUNED LAYER STACK AND METHOD OF MANUFACTURE

1 . A bulk acoustic wave (BAW) device comprising:

a piezoelectric layer;

a first top electrode on a top side of the piezoelectric layer in a first region of the piezoelectric layer;

a second top electrode on the top side of the piezoelectric layer in a second region of the piezoelectric layer;

an acoustic mirror on a bottom side of the piezoelectric layer; and

a bottom electrode between the acoustic mirror and the piezoelectric layer,

wherein the piezoelectric layer comprises a recess on the bottom side in the second region of the piezoelectric layer.

2 . The BAW device of claim 1 , wherein the bottom electrode is disposed in the recess on the bottom side of the piezoelectric layer.

3 . The BAW device of claim 1 , wherein the bottom electrode comprises:

a first bottom electrode disposed in the recess in the second region of the piezoelectric layer; and

a second bottom electrode disposed in the first region of the piezoelectric layer.

4 . The BAW device of claim 1 , wherein a surface on the top side of the piezoelectric layer is planar.

5 . The BAW device of claim 1 , wherein the acoustic mirror comprises a first material disposed in the recess.

6 . The BAW device of claim 1 , wherein the acoustic mirror comprises:

a first material disposed on the bottom electrode;

a first layer of a second material disposed on the first material at a first distance from the top side of the piezoelectric layer in the first region; and

a second layer of the second material disposed on the first material at a second distance from the top side of the piezoelectric layer in the second region.

7 . The BAW device of claim 6 , wherein:

the first distance is greater than the second distance.

8 . The BAW device of claim 1 , further comprising:

a substrate coupled to the acoustic mirror.

9 . The BAW device of claim 8 , further comprising a bonding interface between the acoustic mirror and the substrate.

10 . The BAW device of claim 1 , further comprising:

a first lateral acoustic feature disposed around a perimeter of the first top electrode; and

a second lateral acoustic feature disposed around a perimeter of the second top electrode.

11 . The BAW device of claim 1 integrated into a device selected from the group consisting of: a set-top box; an entertainment unit; a navigation device; a communications device; a fixed location data unit; a mobile location data unit; a global positioning system (GPS) device; a mobile phone; a cellular phone; a smartphone; a session initiation protocol (SIP) phone; a tablet; a phablet; a server; a computer; a portable computer; a mobile computing device; a wearable computing device; a desktop computer; a personal digital assistant (PDA); a monitor; a computer monitor; a television; a tuner; a radio; a satellite radio; a music player; a digital music player; a portable music player; a digital video player; a video player; a digital video disc (DVD) player; a portable digital video player; an automobile; a vehicle component; avionics systems; a drone; and a multicopter.

12 . A method of making a bulk acoustic wave (BAW) device, the method comprising:

forming a piezoelectric layer on a first substrate;

forming a recess in a second region of the piezoelectric layer;

forming a bottom electrode on the piezoelectric layer;

forming an acoustic mirror comprising a first material on the bottom electrode;

planarizing the first material to form a bonding surface;

bonding a second substrate to the bonding surface;

removing the first substrate; and

forming a first top electrode in a first region of the piezoelectric layer and forming a second top electrode in the second region of the piezoelectric layer.

13 . The method of claim 12 , wherein forming the piezoelectric layer comprises growing the piezoelectric layer on a seed layer.

14 . The method of claim 13 , wherein the seed layer comprises at least one of metallic aluminum (Al) and aluminum nitride (AlN).

15 . The method of claim 12 , wherein:

the piezoelectric layer comprises a first thickness in the first region; and

forming the recess comprises thinning the piezoelectric layer to a second thickness in the second region.

16 . The method of claim 12 , wherein forming the bottom electrode comprises forming the bottom electrode on the piezoelectric layer in the first region and in the recess in the second region.

17 . The method of claim 12 , wherein forming the bottom electrode comprises forming a first bottom electrode on the piezoelectric layer in the first region and forming a second bottom electrode in the recess in the second region.

18 . The method of claim 12 , wherein forming the acoustic mirror comprises:

forming the first material on the bottom electrode;

forming a first layer of a second material on the first material in the first region;

forming a second layer of the second material on the first material in the second region; and

forming the first material on the first layer and the second layer.

19 . The method of claim 12 , wherein forming the first top electrode and the second top electrode comprises:

forming a first lateral acoustic feature in the first region of the piezoelectric layer before forming the first top electrode; and

forming a second lateral acoustic feature in the second region of the piezoelectric layer before forming the second top electrode.

20 . A bulk acoustic wave (BAW) device comprising:

a piezoelectric layer;

a first top electrode on a top side of the piezoelectric layer in a first region of the piezoelectric layer;

a second top electrode on the top side of the piezoelectric layer in a second region of the piezoelectric layer;

an acoustic mirror on a bottom side of the piezoelectric layer; and

a bottom electrode between the acoustic mirror and the piezoelectric layer, the bottom electrode having a first thickness in the first region of the piezoelectric layer and a second thickness different than the first thickness in the second region of the piezoelectric layer.

21 . The BAW device of claim 20 , wherein the acoustic mirror comprises:

a first material disposed on the bottom electrode;

a first layer of a second material disposed on the first material in the first region; and

a second layer of the second material disposed on the first material in the second region,

wherein a first distance from the first layer of the second material to the first top electrode is greater than a second distance from the second layer of the second material to the second top electrode.